Computer users, and especially users of portable computing devices, often connect their computers to different computer networks at different times. These computer networks may be at different locations at a computer user's workplace, such as on different floors of a building, or may be at other locations such as the user's home, airports that the user travels through, and other public and private venues that allow computer network access, and especially Internet access, using wired or wireless connection methods. Unfortunately, connecting to a malicious network or a network that is owned by a malicious attacker might jeopardize sensitive information belonging to the user that is stored in the user's computer. In one particular type of network eavesdropping technique known as a “Man-in-the-Middle” attack, an attacker sets up a computer network, such as a wireless computer network in an airport, to which an unsuspecting computer user connects a portable computer. When the computer user uses a web browser to access web-based information such as the user's bank account, the attacker acts as a conduit for information flow between the computer user and the accessed web site, allowing the attacker to record any private information that the user and the web site exchange, such as cookies, passwords, etc. In some instances the attacker can access private information stored on the user's computer even when the user does not initiate the transmission of such information, and can even store malicious data, such as cookies or cache, onto the user's computer.